Thanks grim Reaper
In my case the leisure batteries will be under the seats, the distribution board is just behind the drivers seat and the DC/DC charger will either be with one of the batteries or very nearby.
Installed in the van is as follows:
CBE PC210 Controller
CBE CB516 Mains charger
CBE DS120-S Mains consumer unit
CBE DS300 Distribution board
Waeco CRX 50 Fridge (1.1 to 1.7 amps per hour)
Planar 2D diesel heater - using PU-27 Control panel (apparently 2.4 amps per hour, plus presumably start up amps!)
8 x LED ceiling lights (no idea of amps/watts used, presume negligible)
1 x 550mm LED strip light (no idea of amps/watts used, presume negligible)
Comet submersible pump for cold tap (10 – 24 watts)
Couple of USB charging points for iPad, iPhone and occasional laptop charging.
Any advice on how wire diameter is decided appreciated. I have read before that over specing of the cable can approve efficiently which I’m also willing to consider doing if it seems worth it.